Erickson G F, Nakatani A, Ling N, Shimasaki S
Department of Reproductive Medicine, University of California-San Diego, La Jolla 92093-0625.
Endocrinology. 1992 Feb;130(2):625-36. doi: 10.1210/endo.130.2.1370792.
We have previously shown that the mRNA for insulin-like growth factor-binding protein-4 (IGFBP-4) is present in adult rat ovaries, being localized predominantly to granulosa cells of atretic follicles. Now we have considered the following questions. What class of atretic follicles expresses IGFBP-4 mRNA? How does IGFBP-4 mRNA expression change during the estrous cycle? In keeping with our earlier work, a strong hybridization signal for IGFBP-4 mRNA was present in subpopulations of follicles throughout the estrous cycle. In all cases, the hybridization signal was localized to granulosa cells. Among the various types of follicles, IGFBP-4 mRNA was present almost exclusively in atretic graafian (antral) follicles. Morphologically, the outer layer of granulosa cells was positive, while cells in the cumulus oophorous were negative. By Northern analysis and in situ hybridization, the levels of IGFBP-4 mRNA were found to change over the estrous cycle. At 1000 h on proestrus (before the LH/FSH surge), the hybridization signal was relatively weak, being restricted in some (but not all) atretic Graafian follicles. At 2000 h on proestrus, (after the LH/FSH surge), essentially all atretic Graafian follicles were strongly positive for the message. The pattern of hybridization was similar at 0200 h on estrus, but the signal was less intense. At 1000 h on estrus, the hybridization signal was variable, ranging from very strong to weak or undetectable in atretic follicles. At this stage, however, the highest levels of IGFBP-4 mRNA were measured by Northern analysis; interestingly, a strong signal became apparent in the stromal cells. On diestrous day 1, the message levels decreased, and the signal was restricted to some atretic follicles. On diestrous day 2, the hybridization signal was very weak. There was virtually no detectable IGFBP-4 mRNA in any healthy follicle. In summary, we found that IGFBP-4 mRNA is 1) not detected in healthy dominant follicles; 2) localized almost exclusively to atretic Graafian follicles, except on estrus when it also appears in stromal cells; 3) localized predominantly to the mural granulosa cells in atretic follicles; and 4) undergoes changes during the cycle, being most prominent around estrous morning. The possibility that IGFBP-4 plays a role in the cyclic destruction of cohort Graafian follicles at estrus, perhaps by mechanisms involving hormones, is discussed.
我们之前已经表明，胰岛素样生长因子结合蛋白4（IGFBP - 4）的mRNA存在于成年大鼠卵巢中，主要定位于闭锁卵泡的颗粒细胞。现在我们思考了以下问题。哪类闭锁卵泡表达IGFBP - 4 mRNA？IGFBP - 4 mRNA表达在发情周期中如何变化？与我们早期的研究一致，在整个发情周期的卵泡亚群中都存在针对IGFBP - 4 mRNA的强杂交信号。在所有情况下，杂交信号都定位于颗粒细胞。在各类卵泡中，IGFBP - 4 mRNA几乎仅存在于闭锁的格拉夫卵泡（腔卵泡）中。从形态学上看，颗粒细胞外层呈阳性，而卵丘中的细胞呈阴性。通过Northern分析和原位杂交发现，IGFBP - 4 mRNA的水平在发情周期中会发生变化。在发情前期1000 h（LH/FSH峰之前），杂交信号相对较弱，仅在一些（但不是全部）闭锁的格拉夫卵泡中出现。在发情前期2000 h（LH/FSH峰之后），基本上所有闭锁的格拉夫卵泡对该信息都呈强阳性。发情期0200 h时杂交模式相似，但信号强度较弱。在发情期1000 h时，杂交信号变化不定，在闭锁卵泡中从非常强到弱或无法检测到。然而在此阶段，通过Northern分析测量到IGFBP - 4 mRNA的水平最高；有趣的是，在基质细胞中出现了强信号。在间情期第1天，信息水平下降，信号仅局限于一些闭锁卵泡。在间情期第2天，杂交信号非常弱。在任何健康卵泡中几乎检测不到IGFBP - 4 mRNA。总之，我们发现IGFBP - 4 mRNA：1）在健康的优势卵泡中未检测到；2）几乎仅定位于闭锁的格拉夫卵泡，发情期除外，此时它也出现在基质细胞中；3）在闭锁卵泡中主要定位于壁层颗粒细胞；4）在周期中会发生变化，在发情期早晨最为明显。文中讨论了IGFBP - 4可能通过涉及激素的机制在发情期对成群格拉夫卵泡的周期性破坏中发挥作用的可能性。
